Currently there still exists a high rate of incidence of heart attacks. Angiography, as classically performed by interventional cardiologists or radiologists using a catheter-based, minimally invasive technique, is based on acquiring images of arteries. Using a contrast dye or agent as a mimicking substance for blood, images depicting flow can thus be recorded and physicians may base their diagnosis and subsequently their therapy upon these data. A coronary angiogram is indeed a useful imaging technique but it cannot predict heart attacks well enough. Techniques that can provide more information are invasive, more expensive or have an unproven benefit, e.g. thermography, virtual histology, intravascular ultrasound (IVUS), fractional flow reserve (FFR), palpography, etc. Coronary angiograms contain more information than currently is being used, since it is mostly used to diagnose the severity of stenosis (i.e. abnormal narrowing in a blood vessel). Above 70% stenosis, a percutaneous coronary intervention (PCI) is usually performed on the patient. Below 70% stenosis, first extra info would be welcome. The flow information from angiograms is generally not used at all, while the medical literature has extensively shown that regions of slow flow, regions of altered shear stress, and zones of prolonged contrast agent stasis may account for development of atherosclerotic plaque, rapid progression of atherosclerosis into vulnerable plaque, occurrence of thrombosis and subsequent myocardial infarction, and underdeployment of stents (potentially causing detrimental events such as acute or subacute stent thrombosis). Currently, there are no possibilities to quantify the shear stress in a zone of a blood vessel system in order to provide a risk level of stasis in that zone.
Additionally, the assessment of angiograms is typically paired with a reasonably high level of subjectivity, despite the obvious skills of an aptly trained physician. It is therefore desirable to overcome this problem via a computer application that allows for an objective analysis of angiograms, and more specifically a correct identification of zones of stasis.
Document US 2013-0237815 A1 (D1) discloses a method for determining a four-dimensional angiography dataset describing the flow of contrast agent over time through a blood vessel system of the body of a patient. The four-dimensional flow information is obtained from two-dimensional images captured in a time period in different projection directions using a biplanar x-ray device in an inflow phase and/or an outflow phase of the contrast agent by back projection of the images. The document further discloses that it is conceivable to “automatically undertake a quantitative evaluation of the four-dimensional angiography dataset, for example with regard to flow rates through individual vessels or vessel sections of the vascular system and the like. Such automatic evaluation operations, for example with regard to the cerebral blood flow, are fundamentally already known in the prior art but in the context of the present application can also be carried out on the basis of a dimensional angiography dataset describing the variation with time in high resolution in the three-dimensional space.”.
Document US 2013-0253895 A1 (D2) discloses a system and method for quantifying absolute blood volume flow rates by fitting a kinetic model incorporating blood volume, bolus dispersion and signal attenuation to dynamic angiographic data. The method involves acquiring and fitting dynamic angiographic data to a kinetic model to derive parameter maps. A calibration factor is determined using angiographic data to convert the relative blood volume to an absolute blood volume. The parameter maps are used to simulate the expected signal that arises from a bolus of labelled blood with a short duration relative to the dispersion of the bolus in absence of signal decay. The simulated signals are added and converted into the absolute blood volume. An absolute blood volume flow rate within a vessel mask is determined from blood volume and bolus duration. Using this method, time of arrival of the contrast agent to one or more blood vessels can be compared to each other and to a simulated time of arrival in order to assess a level of stenosis.
Document US 2013-0345559 A1 (D3) discloses a quantitative perfusion analysing method which involves injecting a contrast agent into one or more vascular vessels. A set of angiography images is obtained in a time series and associated with flow of the contrast agent in one or more vascular vessels. The time of arrival of the contrast agent is calculated at each selected location associated with the vascular vessels to present the time of arrival to a user.
Document WO 2010/018500 A1 (D4) discloses a method for dynamically visualizing coronary information and an apparatus adapted to implement such method. In a preferred embodiment of the method, first dynamic cardiac data is acquired during a first cardiac stage and second dynamic cardiac data is acquired during a second cardiac stage. Then, the two data sets are visualized continuously in a superimposed presentation, wherein the first cardiac data and the second cardiac data corresponding to a same phase within the cardiac cycle are visualized simultaneously. In this way for example information about the vessel geometry may be immediately linked with information about the muscle irrigation or perfusion. Furthermore, this information may be displayed in a high-contrasted and low-noise presentation.
Document WO 02/22011 A1 (D5) discloses a method for pictorially depicting and diagnosing thrombi and to the use of particle suspensions for producing contrast agents for depicting thrombin by means of nuclear spin tomography.
There remains a need in the art for an improved identification and diagnose of zones of stasis in blood vessel systems, more in particular for coronary blood vessel systems. The present invention aims to resolve at least some of the problems mentioned above. The invention thereto aims to provide a computer-implemented method for identifying zones of stasis in blood vessels, in order to prevent coronary obstructions from happening.